Ion producing mechanism



W. M. BROBECK ION PRODUCING MECHANISM Filed Nov. 6, 1945 Feb. 28, 1956 ATTORNEY.

United States Patent" IoNrRoDUcmG MECHANISM William M. Brubeck, Berkeley, Calif., assignor to the United States of America as represented by the United States Atomic Energy Commission Application November 6, 1945, Serial No. 627,072

2 Claims. (Cl. 256-413) projected ion beam so that it travels an arcuate path.

Inasmuch as the ions of isotopes of different mass are differently affected by the flux, it has been the practice to so dispose a receiver that one pocket is provided to in v tercept the inner portion of the transmitted beam and a second pocket is arranged to intercept the outer segment of the beam. The material collected in either pocket will be found to vary radically in the concentration of the isotopes constituting the original charge material. That is to say, the material found in one of the pockets will be considerably enhanced with respect to its percentage of a lighter isotope, whereas the other pocket will contain a material considerably impoverished with respect to the lighter isotope.

It has been customary to introduce vapors from a polyisotopic charge material into a restricted passage through which an electron arc discharge travels, the impact of the electron stream upon the particles of the vapor causing ionization of the vapor particles. A pair of accelerating electrodes are disposed adjacent the outer end of the restricted passage, and by applying to the accelerating electrodes a very high voltage, negative with respect to the walls of the restricted passage, positive ions are withdrawn from the plasma in the region of the arc and accelerated to a high velocity. The withdrawn and accelerated ions are projected by the accelerating electrodes through the tank in the form of a relatively narrow rib- .bon or beam.

.It has been the custom to provide a metal block having a chamber for the reception of a charge of a polyisotopic material, in one wall of which chamber there is a narrow slit. A filamentary electron-emissive cathode is disposed directly above the upper end of the slit and operates to discharge a stream of electrons down through the slit when the filament is rendered a few volts negative with respect to the block. The magnetic flux within the tank or vessel serves to collimate the electrons stream from the filament so that the emission is not at random but confined to a relatively narrow pencil traversing the slit.

For a long time, considerably difliculty was experienced in producing an arc discharge which would travel along a predetermined path; that is to say through the slit in the block. Many experiments were made on the basis of a belief that the rate at which the polyisotopic material was vaporized would control the conditions necessary to the generation of an arc discharge. That is to say, there must be supplied to the region through which the arc is rial.

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that the disposition and spacing of the filament was a critical factor, and many attempts were made 'to-produce an eflicient and easily operated arc discharge .device. fl have discovered that the most important factor militating against the generation of an arc discharge through the slit in the block was the influence of .the strong field existing between the block and the accelerating electrodes and between the accelerating electrodes and the filament. The field interfered substantially with the electron discharge from the filament.

Accordingly, it is the object of my invention to elimimate in a calutron ion generatorthe influence of the accelerating electrodes upon the filament and the electron stream traveling from the filament to the block.

An important feature of my invention resides in a shield interposed between the filament (and the space between the filament and the block) and the accelerating electrodes.

I have found that ion producing mechanism equipped with the shield not only exhibits the advantage of protecting the filament from the blocking 'efiect of the accelerating electrodes, but also protects the filament from bombardment by ions.

These and other objects and features of my invention avill be more readily understood and appreciated from Imechanism constructed :in accordance with my invention.

Reference is made to an application for Letters Patent of the United States, filed October 9, 1944, under Serial No. 557,784, by Ernest 0. Lawrence, and now Pat. No. 2,709,222, issued May 24, 1955, for a complete disclosure of the structure and theory of operation of a calutron. It is to be understood that the ion producing mechanism herewith described is designed to be incorporated in .a .calutron of the type disclosed in said application.

As shown in the figure, the ion producing mechanism of my invention is organized about a substantially rectangular-block 10 of steel, copper, or other suitable mate- The block is provided with an internal chamber 12 adapted to receive a quantity or charge 14 of polyisotopic ,material. For example, UF; may be placed in .the chamber 12 if it is desired to utilize the calutron for the separation of uranium into its constituent isotopes. In the rear of the block there is mounted an electric heating element 16, the purposeof which is to heat the charge material 14 and vaporize it. The power supply leads for the heater 16 are indicated diagrammatically at 18. The rear face of theblock 10 is secured toa stem 20, by means of which the block may be mounted in proper location inside the tank or vessel of a calutron. In one of the side walls of the chamber 12 a long, narrow slot '22 is cut-or milled and afiords access from the chamber 12 to the exterior of the'block. Y

Disposed outside the block 10 and adjacent the slit 22 there are located a pair of accelerating electrodes 24. By

Extending across the top of the block and serving as a cover plate for the chamber 12 is an elongated metal plate 32, secured to the top of the block 10 by a pair of screws 34 and having an integral, upwardly extending flange 36 interposed between the accelerating electrodes 24 and the filament 26. Furthermore, the flange 36 lies between the accelerating electrodes 24 and the gap existing between the filament 26 and the top of the block. The

plate 32 is provided with a hole 38 disposed to overlie between the filament 26 and the block 10. The accelerating electrodes 24 are rendered highly negative with respect to the block 10. The voltage drop employed varies extensively in accordance with factors which require no discussion here. It is sufiicient to say that a voltage drop between the accelerating electrodes 24 and the block 10 may exceed 50 kv.

When a charge 14 has been placed in the chamber 12 and the heater 16 energized to cause vaporization of the charge material, particles of vapor will proceed from the chamber 12 through the slot 22. It is to be understood that the tank within which the apparatus is located is constantly serviced by vacuum pumps, and the suction thereby created causes the vapor particles to leave the chamber 12 by way of the slot 22. Assuming now that the circuits have been closed to render the filament and accelerating electrodes negative with respect to the block 10, as previously outlined, a stream of electrons, collimated by the magnetic flux within the tank, will travel from the filament 26 down through the hole 38 and through the slot 22. Vapor particles in the slot 22 will be ionized by the electron arc discharge through the slot, and the positive ions thus formed will be withdrawn from the slot 22 and accelerated across the voltage drop existing betwen the block 10 and the accelerating electrodes 24. The withdrawn and accelerated electrons will be projected between the spaced accelerating electrodes in the form of a narrow ribbon or beam. The magnetic flux within the calutron tank bends the beam so that it follows an arcuate path. The arrow 40 indicates diagrammatically the initial portion of the path traversed by the beam of ions. Ions of lighter isotopes will be more affected by the magnetic flux, and accordingly will be found more copiously distributed along the inner periphery of the curved path; whereas the heavier isotopes are less affected by the magnetic flux and tend to congregate along the outer periphery of the curve. As stated previously, a receiver may be interposed in the path of the beam and provided with pockets to collect different segments of the beam and thus to form segregable masses in which the initial distribution of isotopes has been radically altered. For example, if UF4 is used as a charge material, there will be found in the pocket interposed to collect material from the inner segment of the beam a quantity of material in which the percentage of the isotopes U and U is greater than that in the original charge material. In another pocket there may be collected a material in which the percentage of U has been increased while the percentage of U and U have been decreased.

Ion producing mechanism of the type described is much more efiicient and much more easily started than mechanisms heretofore used, and the increase in efliciency an ease of operation is attributed to the action of the shield 36 which protects the filament and electron stream from the blocking effect resulting from the influence of the highly negative accelerating electrodes 24.

Having now described and illustrated an embodiment of my invention, what I claim as new and desire to secure by Letters Patent of the United States is:

1. Ion producing mechanism comprising in combination a metallic block disposed in a magnetic field and having an open-ended cylindrical chamber formed therein for containing a source of ionizable vapor, said block being further provided with an open-ended slot elongated in the axial direction of said chamber and constituting a communicating passageway between said chamber and the exterior of said block and in alignment with said magnetic field, an electron emissive filament spaced from said block and aligned with the end of said slot, means impressing a potential between said filament and block whereby an arc discharge is established from said filament through the length of said slot to the end thereof under the influence of said magnetic field, accelerating electrode structure disposed adjacent said slot and externally of said block and maintained at a negative potential with respect to the latter whereby ions formed of said vapor by said arc are attracted from said block, and a shield of rigid sheet material L-shaped in cross-section, having one portion thereof secured to said block in closing relation to the open-end of said chamber and having the remaining angularly disposed portion thereof extending in parallelism with the axis of said chamber and disposed intermediate said filament and said accelerating electrode structure whereby the portion of the arc beyond said block is shielded from the potential of said accelerating electrode structure, said shield being provided with an aperture disposed adjacent the open end of said elongated slot and in substantial registry therewith for the passage of said arc discharge therethrough.

2. In an ion producing mechanism providing an ionizing arc discharge between a filament and a source block along a slot in the latter and means to remove ions from the length of said are in said source block; a shield comprising two right-angularly disposed walls, one only of which is apertured, the apertured wall of said shield being secured to said source block spaced from but adjacent said filament and disposed with the aperture therein in the path of said are discharge, and the other wall of said shield extending between said filament and said ion removal means to provide a continuous protecting barrier for isolating the portion of said are discharge exterior to said source block from said ion removal means.

References Cited in the file of this patent UNITED STATES PATENTS 2,221,467 Bleakney Nov. 12, 1940 2,373,151 Taylor Apr. 10, 1945 2,374,205 Hoskins Apr. 24, 1945 2,378,962 Washburn June 26, 1945 OTHER REFERENCES Tuve et al.: Physical Review, vol. 48 (Aug. 1, 1935), pages 241256 (pages 243 and 244 relied on).

Lamar et al.: Physical Review, vol. 48 (Dec. 1, 1935), pages 886-892 (pages 886, 887 relied on). 

1. ION PRODUCING MECHANISM COMPRISING IN COMBINATION A METALLIC BLOCK DISPOSED IN A MAGNETIC FIELD AND HAVING AN OPEN-ENDED CYLINDRICAL CHAMBER FORMED THEREIN FOR CONTAINING A SOURCE OF IONIZABLE VAPOR, SAID BLOCK BEING FURTHER PROVIDED WITH AN OPEN-ENDED SLOT ELONGATED IN THE AXIS DIRECTION OF SAID CHAMBER AND CONSTITUTING A COMMUNICATING PASSAGEWAY BETWEEN SAID CHAMBER AND THE EXTERIOR OF SAID BLOCK AND IN ALIGNMENT WITH SAID MAGNETIC FIELD, AN ELECTRON EMISSIVE FILAMENT SPACED FROM SAID BLOCK AND ALIGNED WITH THE END OF SAID SLOT, MEANS IMPRESSING A POTENTIAL BETWEEN SAID FILAMENT AND BLOCK WHEREBY AN ARC DISCHARGE IS ESTABLISHED FROM SAID FILAMENT THROUGH THE LENGTH OF SAID SLOT TO THE END THEREOF UNDER THE INFLUENCE OF SAID MAGNETIC FIELD, ACCELERATING ELECTRODE STRUCTURE DISPOSED ADJACENT SAID SLOT AND EXTERNALLY OF SAID BLOCK AND MAINTAINED AT A NEGATIVE POTENIAL WITH RESPECT TO THE LATTER WHEREBY IONS FORMED OF SAID VAPOR BY SAID ARC ARE ATTRACTED FROM SAID BOLCK, AND A SHIELD OF RIGID SHEET MATERIAL "L-SHAPED" IN CROSS-SECTION, HAVING ONE PORTION THEREOF SECURED TO SAID BLOCK IN CLOSING RELATION TO THE OPEN-END OF SAID CHAMBER AND HAVING THE REMAINING ANGULARY DISPOSED PORTION THEREOF EXTENDING IN PARALLELISM WITH THE AXIS OF SAID CHAMBER AND DISPOSED INTERMEDIATE SAID FILAMENT AND SAID ACCELERATING ELECTRODE STRUCTURE WHEREBY THE PORTION OF THE ARC BEYOND SAID BLOCK IS SHIELDED FROM THE POTENTIAL OF SAID ACCELERATING ELECTRODE STRUCTURE, SAID SHIELD BEING PROVIDED WITH AN APERTURE DISPOSED ADJACENT THE OPEN END OF SAID ELONGATED SLOT AND IN SUBSTANTIAL REGISTRY THEREWITH FOR THE PASSAGE OF SAID ARC DISCHARGE THERETHROUGH. 